Introduction of zirconium into magnesium



Feb. 7, 1961 i w, UNSVWQRTH 2,970,904

INTRODUCTION OF ZIRCONIUM INTO MAGNESIUM Filed April 27, 1959 8367 90 80 70 60 5O 4O 3O 20 IO NdC/ ATTORNEY Uflllfid State I the matrix phase.

INTRODUCTION OF ZIRCONIUM INT MAGNESIUM William Unsworth, Clifton Junction, near Manchester, England, assignor to Magnesium Elektron Limited, Clifton Junction, near Manchester, England, a company of Great Britain v 7 Filed Apr. 27, ias9, Ser.No. 809,224 7 Claims priority, application Great Britain May '9, 1958 8 Claims. (Cl. 75-168) This invention relates to the introduction of zirconium into magnesium and in particular to the production of a master alloy for introducing Zirconium into magnesium especially for producing alloys of the kind defined in British Patent No. 511,137 which are substantially free from elements (which may be termed inhibitor elements) which combine with zirconium to form insoluble compounds in a molten magnesium melt, for example aluminium, silicon and iron, but may contain other elements (which may be termed permissible elements) such as zinc, cadmium, thorium, rare earth metals, beryllium, indium, thallium, silver, copper, bismuth, lead and calcium. A smali proportion of manganese can be tolerated; Another use for the master alloy is to precipitateiron or other inhibitor elements from magnesium.

' It has been proposed in British Patent No. 652,222 to prepare such a master alloy consisting of three phases, viz. (1) a salt phase consisting of 1 to 30% by weight of the master alloy, (2) a matrix phase consisting of magnesium with or without permissible elements and zirconium, and (3) a zirconium rich phase embedded in It was indicated that the salt phase might consist of various fluorides and/or chlorides. It was further known from British Patent No. 652,227 that when using alkali metal fiuozirconate as the source of zirconium this must be mixed with some proportion of alkali metal chloride in order to avoid explosion when reacting with magnesium. It was found however that masteralloys produced by this process were not metallic in appearance and contained at least 15 percent (and usually about 25 percent) of the salt phase with the disadvantage that an undue proportion of magnesium became trapped in the salt and so lost. This difliculty can be overcome by using zirconium fluoride instead of fluozirconate and a salt phase consisting wholly of fluorides, but this involves the use of lithium fluoride, which is very expensive, in order to achieve a sufiiciently low melting point. The amount of the salt phase may also be controlled by using zirconium chloride instead of fluozirconate'asdescribed in British Patent No. 652,222, salt phase contents below being fairly readily achieved and the-alloy being more or less of metallic appearance. Zirconium chloride is however volatile, deliquescent, and readily hydrolysed therefore unpleasant to use and difficult to store. Furthermore, master alloys made from it show variations in alloying properties and the resulting alloys do not always fully exhibit the high tensile properties expected of the megnesium zirconium alloys;

'The high salt residue content'which arises when using fiuozirconate was found to be due to the fact that the chloride residues are inspissated by the magnesium fluoride'produced during the reaction with magnesium, as a result of which the chloride residue is not sufi'iciently fluid to enable it to be readily squeezed out of the master. alloy. Since magnesium fluoride is known to be insoluble in alkali metal chlorides, and since mere dilution of the megnesium fluoride with excess of the chloride salts was not found effective, it has for some years been con- 7 may be lost with the salt residue.

2,970,904 Fatented Feb. 7, 1961 ice sidered that the difliculty could not be overcome. The general insolubility of MgF in mixtures of alkali and alkaline earth chlorides is, moreover, well borne out by the literature and by its use to inspissate all manner of chloride-based fluxes for use with magnesium alloys. The inspissating effect of CaF in fluxes based on MgCl is itself a reflection of the. insolubility of MgF in such chloride mixtures. On the other hand, since the unit of zirconium was cheaper in potassium fiuozirconate than in zirconium chloride, and the fiuozirconate was non-volatile, stable in air and readily stored and handled, it was very desirable commercially that the problem of preparing a master alloy with low salt content from fiuozirconate should if possible be solved.

The present invention is based on the discovery that the problem can in fact be solved by providing in the reaction mixture a considerable excess of magnesium chloride in quantity sufficient (a) to react with all of the KP, (b) to react with all the ZrF and (c) to provide in addition enough unreacted magnesium chloride to dilute the alkali metal chlorides to such an extent and to establish such a high concentration of magnesium chloride in the salt phase that the magnesium chloride can largely dissolve the magnesium fluoride produced during the reaction in spite of the alkali metal chlorides present, whereby the salt phase remains fluid and can be pressed out of the master alloy so as to leave a maximum of 10 percent salt phase in the master alloy and usually about 3 to 5 percent. The final master alloy is thus at least as free from entrained salts as that made from chlori e salt mixtures based on zirconium chloride.

Owing 'to the slightly inspissating effect of the residual MgF in the salt phase, the latter tends to be present in a few comparatively large inclusions in the interior of the blocks or ingot into which it is cast, rather than to be widely distributed in small inclusions throughout the mass and spread out in thin films on the metal sur- -face as is the case with master alloy made from the Alkali metal fiuozirconate 1 mol.

MgCl 4.5 to 7.5 mols.

Alkali metal chloride 2.0 to 5.5 mols.

Magnesium metal 7 to 12 gram-atoms to 1 gram/mol fiuozirconate.

' The alkali metal fiuozirconate is preferably potassium fiuozirconate having a ratio of KF to ZrF of from 1.0 to VlZ. KZl'F to KZZI'FG.

The alkali metal chloride is preferably KCl and/or NaCl.

The magnesium metal may be added in two stages, viz: 3 to 5 gram-atoms to 1 mol of fiuozirconate in the first stage to produce a fairly stiff reaction product from which most of the salt residue can be readily expressed, the remainder being then added so as to make a master alloy which is sutficiently fluid to permit its being poured out of the crucible.

If less than 3 gram-atoms of magnesium is used in the first stage the zirconium forms a clinker-like mass and is not taken into solution even when more magnesium is added subsequently and if more than 5 gram-atoms is used in the initial reaction a proportion of the magnesium If desired, some BaCl may be included in the reaction mixture in proportion up to l.5 mols in order to suppress residual flux contamination in the final magnesium-zirconium alloy. I

It is not generally desirable that any other ingredients should be included in the reaction mixture but it is possible also to include permissible elements other than calcium, e.g. replacing up to 60 percent of the magnesium. Beryllium however will not be incorporated in the magnesium in amounts exceeding 0.01 percent by weight of the mixture. Reducible chlorides of permissible elements may also be included in the reaction mixture, e.g. up to 50 percent of the MgCl can be replaced by an equivalent weight of thorium chloride or rare earth metal chloride.

Also according to the invention a 3-phase master alloy is produced having the following composition:

(l) A salt phase consisting of 1 to 10 percent by Weight of the master alloy and containing MgCl and MgF the latter being from 25 to 40 percent by weight of the MgCl together with alkali metal chloride in quantity by weight from one-third to two-thirds the weight of the MgCl with or without BaCl (2) A matrix phase consisting wholly or mainly of magnesium with or without zirconium and/ or permissible elements.

(3) Metallic zirconium embedded in phase (2) and constituting 25 to 45 percent by weight of the master alloy.

The quantity of BaCl preferably does not exceed half the weight of MgCl in the chloride added for the initial reaction. The quantity of BaCl in the final master alloy, therefore, does not exceed twice the weight of the MgF The presence of BaCl assists avoidance of flux particles in the final alloy but too much would unduly increase the melting point of the chloride phase used in the initial reaction which is preferably from 420-600 C.

A particularly desirable range of chloride salt mixtures for the initial reaction is indicated by the area marked A in the accompanying drawing while the area marked B is preferred.

An example of the method of making the master alloy is as follows;

A mixture consisting of 374 lb. MgCl 150 lb. KCl and 136 lb. BaCl was melted and added to 160 lb. of potassium fluozirconate in a separate crucible. The resulting mixture was heated to 650 Cf: at this temperature 65 lbs. of solid preheated magnesium was added and when molten the melt was stirred to bring about the reaction. During stirring, the temperature of the melt rose to 800 C. owing to the strongly exothermic nature of the reaction between magnesium and the ZrCl formed in situ by the reaction of MgCl and KZrF The chrides were decanted away from the pastry zirconium master alloy in the bottom of the crucible. The master alloy was pressed to exclude the entrained chloridefluoride phase and a further 65 lbs. of magnesium was added to dilute the master alloy to a consistency suitable to enable it to be cast into moulds. This melt yielded 165 lb. of zirconium master alloy containing 35 percent zirconium and 3.6 percent chloride.

Experience has shown that the master alloy of the present invention is constant in its alloying properties and gives consistently magnesium zirconium alloys with maximum tensile properties.

Another and unexpected advantage of the product over the corresponding chloride master alloy is its uniformity when molten. When preparing chloride based master alloy containing, for example, 30 precent zirconium, the mass of pasty allcyin the crucible readily separates into an upper fluid and a lower pasty layer on standing, necessitating stirring before casting each block. Segregation of zirconium can also occur in the blocks or ingots into which the master alloy is cast. The fluoride based master alloy of the present invention is however. remarkably homogeneous and showslittle tendency to segregate in the i 4 molten state. This valuable property is illustrated by the following zirconium contents from the top and bottom of ingots of chloride based master alloy sold commercially and applicants fluoride based master alloy.

Zirconium Contents Muster Alloy type Average Top Bottom Commercial chloride based 30 0. 3/7. 2 36.4 Fluoride based in accordance with Applicant's invention 35 39.u 37.3

Alkali metal fluozirconate 1 mol.

MgCl 4.5 to 7.5 mols. Alkali metal chloride 2.0 to 5.5 mols. Magnesium metal 7 to 12 gram-atoms to 1 gram/mol fluozirconate;

to a temperature above the melting point of magnesium.

2. A method as claimed in claim 1 wherein the fluozirconate is potassium fiuozirconate having a ratio of RF to ZrF between 1.0 and 2.0.

3. A method as claimed in claim 1 wherein the alkali metal chloride is at least one chloride selected from the group consisting of potassium chloride and sodium chloride.

4. A method as claimed in claim 1 wherein the magnesium metal is added in two stages in which 3 to 5 gramatoms to 1 mol fluozirconate in the first stage and the remainder after expressing most of the salt residue.

5. A method as claimed in claim 1 wherein some BaCl is included up to 1.5 mols.

6. A method as claimed in claim 1 wherein up to onethird of the magnesium is replaced by at least oneof the elements. zinc, cadmium, thorium, rare earth metals, indium. thallium, silver and beryllium, the beryllium however not exceeding 0.01 percent.

7. A method as claimed in claim 1 wherein up to 50 percent of the MgCl is replaced by a chemically equ|va lent weight of at least one of the chlorides of the elements thorium, rare earth metals and manganese.

8. A master-alloy for introducing zirconiuminto magi;

. nesium comprising beryllium and silver,

and metallic zirconium embedded in saidmatrix phase and constituting 25 to 45 percent by weight of the master alloy. 1

References Gited in the file of this patent UNITED STATES PATENTS 2,497,530 Ball a a1. Feb. 14. 1936 

8. A MASTER-ALLOY FOR INTRODUCING ZIRCONIUM INTO MAGNESIUM COMPRISING A SALT PHASE CONSISTING OF 1 TO 10 PERCENT BY WEIGHT OF THE MASTER ALLOY AND CONTAINING MGC12 AND MGF2, THE LATTER BEING FROM 25 TO 40 PERCENT BY WEIGHT OF THE MGC12, TOGETHER WITH AN ALKALI METAL CHLORIDE IN QUANTITY BY WEIGHT FROM ONE-THIRD TO TWO-THIRDS THE WEIGHT OF THE MGC12, A MATRIX PHASE CONSISTING SUBSTANTIALLY OF MAGNESIUM, AND AT LEAST ON OF THE ELEMENTS ZIRCONIUM, ZINC, CADMIUM, THORIU, RARE EARTH METALS, INDIUM, THALLIUM, BERYLLIUM AND SILVER, AND METALLIC ZIRCONIUM EMBEDDED IN SAID MATRIX PHASE AND CONSTITUTING 25 TO 45 PERCENT BY WEIGHT OF THE MASTER ALLOY. 